a) Field of the Invention
The present invention relates to a semiconductor device and its manufacture method, and more particularly to a semiconductor device having bump electrodes suitable for flip chip bonding and its manufacture method.
With advancement of high integration and multi-function of a semiconductor integrated circuit, the number of connection electrodes of the circuit to an external circuit is increasing. Requirements for compact devices make device assembly use flip chip bonding using bump electrodes.
b) Description of the Related Art
A conventional method of forming bump electrodes will be described with reference to FIGS. 11A and 11B.
As shown in FIG. 11A, on the surface of a semiconductor substrate 200, an insulating film 201 is formed, and a pad 202 made of aluminum (Al) is formed in a partial surface area of the insulating film 201. The other surface area of the insulating film 201 is covered with an insulating film 203. A metal film 204 is formed on the pad 202 and insulating film 203, covering the whole surface of the substrate.
A photoresist film 205 having a thickness of several microns is coated on the metal film 204. An opening 205a is formed through the photoresist film 205 in an area corresponding to the pad 202. On the surface of the metal film 204 exposed at the bottom of the opening 205a, a bump material 206 made of SnPb alloy is deposited through electrolysis plating. The bump material 206 fills the inside of the opening 205a, extends thereafter from the periphery of the opening 205a to the surface area of the photoresist film 205, and shows a mushroom shape.
The photoresist film 205 is thereafter removed and a portion of the metal film 204 not covered with the bump material 206 is etched and removed.
As shown in FIG. 11B, a reflow process is performed by heating the substrate so that the bump material of the mushroom shape changes to generally a sphere shape. In the above manner, the bump electrode 206 is formed on the pad 202.
With the conventional method described above, when the bump material is deposited through plating, the bump material 206 takes the mushroom shape expanding around the pad 202 as shown in FIG. 11. Therefore, if the pitch between pads becomes small, adjacent bump electrodes are likely to contact each other. It is difficult to arrange uniformly for the height of bump electrodes 206 having generally the sphere shape shown in FIG. 11B.
Although a method of forming a solder ball on a pad through a transfer process is known, also this method is difficult to deal with a fine pitch between pads.